Investigation on the bending behaviors of reinforced thermoplastic pipes using a strain energy equivalence method and a continuum damage numerical model

Abstract This paper investigates the bending stiffness and progressive failure of reinforced thermoplastic pipes (RTPs) under bending loads, in which a theoretical method based on the strain energy equivalence of multi‐layered anisotropic cylinders, is proposed. The bending stiffness and stress field was derived from the equilibrium between the work done by bending moments and the strain energy. This new method could consider the hybrid of isotropic and anisotropic materials and improve computation efficiency significantly. To verify the theoretical method, Abaqus/Explicit quasi‐static analysis on 3D composite elements was performed, in which the progressive failure was considered by using a VUMAT subroutine. The degradation of composites was implemented by a nonlinear stiffness degradation model based on the Hashin‐Yeh failure criterion. The comparison showed that the theoretical results are slightly conservative as the theoretical method neglects the contribution of interlayer interactions. Meanwhile, it can accurately predict the dominant stresses of each composite lamina. According to numerical simulations, the fiber tensile failure, the matrix tensile and compressive failure are the dominant failure modes of RTPs under bending loads. Furthermore, the effects of the winding angles of fibers on damage propagation and the effects of the initial ovality on the bending stiffness are also discussed.